Cross-technology interference is emerging as a major problem for 802.11 networks. Independent studies show that high-power interferers like baby monitors and cordless phones can cause 802.11n networks to experience a complete loss of connectivity, and that such interferers are responsible for more than half of the problems reported in customer networks. Today's high-power non-WiFi sources in the ISM band include surveillance cameras, baby monitors, microwave ovens, digital and analog cordless phones, and outdoor microwave links. Some of these technologies transmit in a frequency band as wide as 802.11, and all of them emit power that is comparable or higher than 802.11 devices. Further, the number and diversity of such interferers is likely to increase over time due to the proliferation of new technologies in the ISM band.
Empirical studies of cross-technology interference show the following:                High-power cross-technology interference can completely throttle 802.11n. Furthermore, loss of connectivity can occur even when the interferer is in a non-line-of-sight position and separated by 90 feet.        While 802.11 and low-power interferers (e.g., Bluetooth) have managed a form of coexistence where both devices stay operational, coexistence with high-power devices (e.g., cordless phones, baby monitors, microwave, etc.) is lacking. Furthermore, the typical outcome of the interaction between 802.11n and a high-power interferer is that 802.11n either suffers a complete loss of connectivity or a significant throughput reduction. Even if carrier sense is deactivated, 802.11n continues to lose connectivity for many of the interferer's locations.        Frequency isolation is increasingly difficult. Multiple of the studied interferers occupy relatively wideband channels of 16-25 MHz (e.g., camera and microwave). Moreover, these devices can occupy any band in the 802.11 spectrum. For example, both the cordless phone and the baby monitor have multiple channels that together cover almost the whole frequency range of 802.11.        Finally, the characteristics of an interferer may change in time and frequency. The interferer may have ON-OFF periods, may move from one frequency to another, or change the width of the channel it occupies, like a microwave. This emphasizes the need for an agile solution that can quickly adapt to changes in the interference signal.        
Wireless interference has been the topic of much recent research. Work in this area falls under two broad categories:
A first category addresses interference across technologies. One can identify three main approaches within this category. The first approach attempts to eliminate interference by isolating the signals in time, frequency or space. The most common isolation approach is to employ frequency-based isolation, such as OFDM subcarrier suppression [16, 11, 14], variable channel width [4], or other fine grained frequency fragmentation techniques [19, 12, 10]. Directional antennas may also be used to provide spatial isolation and reduce interference. However, directional antennas are difficult to use in indoor scenarios where the signal tends to bounce off walls and furniture and scatter around [18].
The second approach uses mitigation schemes to modify transmissions to be more resilient to interference (e.g. by using coding or by lowering the bit rates). Mitigation proposals like PPR [8] and MIXIT [9], though designed and evaluated for the same technology, can work across technologies. These schemes however assume interference is fairly transient and limited to some bytes in each packet.
Finally, some proposals identify the type of interference (e.g., is the interference from ZigBee or Bluetooth?) and inform the user so they may switch off the interfering device [2]. Others leverage the specific characteristic of a particular technology to design a suitable coexistence strategy [5].
A second category addresses interference from the same technology. Recent work in this category include interference cancellation [13], ZigZag [6] and analog network coding [15] which address the problem of interference from other 802.11 nodes. Prior work on MIMO systems enables multiple transmitters to transmit concurrently without interference. This includes schemes like SAM [17], Interference Alignment and Cancellation [7], and beamforming systems [3].
Finally prior work on interference management in cellular networks uses multiple antennas to mitigate interference from nodes operating in adjacent cells [18, 1].